1 SCINTILLATION LIGHT YIELD OF Ce-ACTIVATED LSO, LYSO, LuAP AND LuYAP

2 AUTHORS: Andrzej J. Wojtowicz and Winicjusz Drozdowski N. Copernicus University (UMK) Research, characterization of scintillator materials Jean-Luc Lefaucheur, Zbigniew Galazka and Zhenhui Gou Photonic Materials Ltd (PML) R&D on LYSO:Ce, LuAP:Ce, LuYAP:Ce PML manufactures LYSO and is the only company supplying large LuAP and LuYAP crystals on commercial scale

3 CRYSTALS: LSO (Lu 2 SiO 5 :Ce, oxyorthosilicate) 2x2x10 pixels, grown by CTI Inc, provided by dr C. Melcher, dr P. Lecoq, dr C. Kuntner, prof. S. Tavernier LYSO (Lu 2(1-x) Y 2x SiO 5 :Ce, oxyorthosilicate), LuAP (LuAlO 3 :Ce, aluminum perovskite), LuYAP (Lu x Y 1-x AlO 3 :Ce, x=0.7, aluminum perovskite) 2x2x10 pixels and 5x5x1 plates grown by PML

4 SCINTILLATION LIGHT YIELD and ENERGY SPECTRA Incoming gamma particle may: get absorbed by giving up all its energy to a single electron (photoelectron) get scattered away by a single electron (Compton electron) and escape Energy of (photo- or Compton) electron is transformed into scintillation Scintillations differ; a plot showing number of scintillations (y axis) vs amount of light in a single scintillation (x axis) is called energy spectrum

5 Hamamatsu R V, Cs 137 (662 keV), spectr. ampl. gain 3, note photopeak, Compton edge, backscatter peak Energy spectrum, BGO, pixel 2x2x10mm, vertically

6 Energy spectrum LSO 1050 CTI 2x2x10 mm pixel vertically Hamamatsu R2059 (1500 V) Na-22 (511 i 1274 keV) spectr. ampl. gain 3 Note: two photopeaks and two Compton edges, the third developing peak (between 800 and 1000) and edge (at 720)

7 Light yield measurement: standard method LSO 1050 CTI and two BGO 2x2x10 mm pixels, vertically Hamamatsu R2059 (1500 V) Cs 137 (662 keV) and Na22 (511, 1274 keV)

8 Energy spectra BGO „old” 2x2x10 vertically Hamamatsu R2059 (1500 V) Cs137 (662 keV) spectr. ampl. gain variable Note: photopeaks shift with gain

9 Photopeak positions vs spectr. ampl. gain; PP vs G) BGO „old” 2x2x10 pixel R V, Cs 137 (662 keV) note offset y0 Photopeak position at 1 MeV: 12.0/0.662 = 18.1

10 Energy spectra BGO „new” 2x2x10 vertically Hamamatsu R2059 (1500 V) Na 22 (511, 1274 keV) spectr. ampl. gain variable Note: photopeaks shift with gain

11 Photopeak positions vs spectr. ampl. gain (PP vs G) BGO „new” 2x2x10 pixel R V Na22 (511, 1274 keV) note offset y 0

12 Energy spectra LSO x2x10 vertically Hamamatsu R2059 (1500 V) Cs 137 (662 keV) spectr. ampl. gain variable

13 Photopeak positions (PP) vs spectr. ampl. gain (G) (PP vs G) LSO x2x10 R V Cs 137 (662 keV) Photopeak position at 1 MeV: 96.7/0.662 = 146.1

14 STANDARD METHOD; summary of LSO 1050 Does it work well? What if we change the voltage? This can’t be right! LY must be constant!

15 Let us see if we can understand what is wrong. The signal from the PMT should look like this: S is a signal at PMT, V voltage, K number of photoelectrons at photocathode, n number of PMT stages, and α constant (assumed different in each case)

16 from these expressions for Ss it follows that: and now we see why the ratio of Ss for LSO and BGO depends on V; this is because alphas are different. Now, does it make sense, can they really be different? Different scintillators produce different load on photocathode distributed differently in time

17 Photopeak position fits: LSO 1050 Y = X^ * E keV BGO old Y=X^9.05*3.31 BGO new Y = X^9.16* 1.89E-028, 511 and 1274 keV S LSO and S BGO vs PMT voltage

18 SUMMARY of results from fits:

19 SUMMARY of results from fits: No systematic dependence on V. Fits give good averaged LY value from a number of spectra

20 ENERGY SPECTRA and scintillation light yield: LYSO (PML) 3h energy spectrum of LYSO 2x2x10 vertically R2059, 1500 V, Na 22 the best pixel so far Energy resolution: 12.2% (511 keV) 7.3% (1274 keV)

21 ENERGY SPECTRA and scintillation light yield: LYSO (PML) 3h energy spectrum of LYSO 2x2x10 horizontally R2059, 1200 V, Na 22 the best pixel so far Energy resolution: 11.3% (511 keV) 7.6% (1274 keV) 6.9% (1785 keV) Note the third peak The vertical/horizontal ratio 0.61, the highest ever

22 ENERGY SPECTRA and scintillation light yield: LYSO (PML)

23 ENERGY SPECTRA and scintillation light yield: LYSO (PML)

24 ENERGY SPECTRA and scintillation light yield: LuAP (PML) LuAP plate, 5x5x1 (PML) R2059, 1500 V, spectr. ampl. gain 3, Na22 note the third peak

25 ENERGY SPECTRA and scintillation light yield: LuAP (PML) LuAP plate, 5x5x1 (PML) R2059, 1500 V, spectr. ampl. gain 3, Na22 note the third peak

26 ENERGY SPECTRA and scintillation light yield: LuAP (PML) LuAP plate, 5x5x1 (PML) R2059, 900 V, spectr. ampl. gain 300, Na22 note the third peak

27 ENERGY SPECTRA and scintillation light yield: LuAP (PML) LuAP plate, 5x5x1 (PML) R2059, 900 V, spectr. ampl. gain 300, Na22 note the third peak

28 ENERGY SPECTRA and scintillation light yield: LuAP (PML) LuAP plate, 5x5x1 (PML) R2059, 1500 and 900 V, Na22

29 ENERGY SPECTRA and scintillation light yield: LuYAP (PML) LuYAP plate, 5x5x1 (PML) R2059, 1500 V, spectr. ampl. gain 3, Na22

30 SUMMARY We have developed a new method to measure scintillation light yield of scintillator materials The method, unlike the standard method, requires that a number of spectra for different amplifier gains and PMT voltages are measured The method takes into account offset of energy spectra and unexpected voltage dependence and provides good undistorted values

31 The method has been used to study a representative set of LYSO, LuAP and LuYAP crystals grown by PML The LYSO developed by PML reached a mature stage; the best LYSO pixel is by 50% brighter than a good LSO pixel 1050 LuYAP and LuAP crystals developed by PML show LYs that are comparable (LuAP slightly ahead) The important source of loss of light must be some unidentified absorption centers that quench scintillation in longer samples